The present invention relates to a sampling device for gas analyzers using gas detectors such as a FID (Flame Ionization Detector) and a CLD (Chemical Luminescence Detector).
Since a quantity of a sample gas entering a detector such as a FID and a CLD is small, i.e. on the order of several cc/min to several 10 cc/min, the inside diameter of a capillary used in the control of the flow rate must be very small, i.e. from 0.1 to 0.3 mm. This creates a difficulty in that the capillary is inclined to be choked by material included in the sample gas.
There is shown in FIG. 4(A) a known, sampling device in which a sample-supply passage 41 is provided with one capillary 42 connected thereto, and in FIG. 4(B) there is shown a known sampling device in which two capillaries 42 and 42' are connected in parallel and selectively changed over by means of a three-way changeover valve 43.
With the conventional sampling device shown in FIG. 4(A), in the event that the capillary 42 is choked, it must be replaced to continue the measuring operation. It takes much time to replace the capillary, and then it takes several further hours to achieve stabilization of the temperature and return to normal of the level of background noise in the detector output after the replacement of the capillary.
As a result, a great problem has occurred in that if the capillary is choked during the measurement, the measurement can not be resumed for a long time due to the necessity for repair, particularly in an on-line measurement such as the measurement of exhaust gas from a car.
Also, with the conventional sampling device shown in FIG. 4(B), in which the capillaries 42 and 42' are connected in parallel, the passage 45 and the valve 43 used for changing over have too large a volume in comparison with the flow rate of the sample sent to the detector 44 through the capillaries 42 and 42' whereby a dead space is formed, so that there is a defect in that it takes a long time to replace the gas and the response speed of the gas analyzer is greatly reduced.